1. Field of the Invention
This invention relates to circuit arrangements and teleprinter apparatus and specifically to a device which can be retrofitted into an existing teleprinter to automatically output dialing pulses in response to a stored multi-digit number.
2. Discussion of Related Art
Many existing teleprinter models are presently in use. These include the M-28 TELEX, M32 TELEX, M33 TWX or M35 TWX and variations of these models. As presently used, these teleprinters are equipped with a rotary dial mechanism which operates a relay causing the outputting of selection pulses which are conducted via a teleprinter line to an exchange system. Use of a rotary dial as described contains many disadvantages. A dial is mechanical and therefore subject to wear. Further each time a number is to be called, each digit of the number must be sequentially inputted manually into the system through use of the dialer.
Various dialing systems for telephones and teleprinters have been suggested. For instance, U.S. Pat. No. 4,000,363, issued Dec. 28, 1976, to Widmaier, shows a teleprinting apparatus which utilizes the keyboard through a coding system to generate pulse trains thereby eliminating the dial switch. A selection pulse generator is supplied with signals from a counter pulse train of constant repetition frequency, the number being determined by the selection of the key on the keyboard. The Widmaier system utilizes digital circuitry; however, no specific provision is disclosed for establishing the appropriate voltage levels for the integrated circuitry. U.S. Pat. No. 3,733,440, issued May 15, 1973, to Sipes, discloses a semiautomatic call placement system wherein wake up messages are delivered automatically to a plurality of telephone numbers which are stored in a memory and dialed automatically at a predetermined time. U.S. Pat. No. 4,143,243, issued Mar. 6, 1979, to Sutton, shows a telephone set which will automatically redial a telephone number after a busy signal has been received and continues redialing that number until the party being called answers, or until a predetermined number of attempts have been made. U.S. Pat. No. 3,956,596, issued May 11, 1976, to Connolly et al., shows a pushbutton telephone semiconductor dialing circuit power supply comprising a capacitor fed by a diode bridge placed in series with the line looping circuit during dialing. The capacitor size is chosen to charge to at least minimum circuit supply voltage during make periods of line looping, and to keep the circuit supplied during break periods. U.S. Pat. No. 3,856,982, issued Dec. 24, 1974, to Lawson et al., discloses a pushbutton unit to replace the dial of a telephone instrument. The pushbutton operation enters dialed digits into an MOS circuit whose outputs operate relays. One of the relays repeats the digits to the line in conventional impulse train form, while the other deals with "off normal" dial functions. The electronics is line powered.